Condensed Balance Sheets (Parenthetical) - USD ($)	Jan. 31, 2022	Apr. 30, 2021
Accounts receivable, allowance for credit loss, current	$ 25,747	$ 9,947
Convertible preferred stock, shares authorized	1,000,000	1,000,000
Class A Common stock, par value	$ 0.10	$ 0.10
Class A Common stock, shares authorized	10,000,000	10,000,000
Class A Common stock, shares issued	8,502,881	8,502,881
Class A Common stock, shares outstanding	8,502,881	8,502,881
Treasury stock, shares	3,559,125	3,556,412
Noncumulative Preferred Stock [Member]
Convertible preferred stock, shares authorized	25,000	25,000
Convertible preferred stock, stated value	$ 20	$ 20
Convertible preferred stock, shares issued	4,100	4,100
Convertible preferred stock, shares outstanding	4,100	4,100